The present invention relates to an original handling apparatus for automatically feeding an original to an original reading position.
In a conventional image forming apparatus such as a copying machine, an original conveying apparatus for automatically feeding an original to an exposure position and discharging the original after an exposure operation is often additionally used.
However, in the conventional original conveying apparatus, the following original conveying method is employed regardless of the size of an original. In this method, an original is fed to and stopped at a copying position on a platen glass one by one, the original for which copying exposure is completed is discharged from the platen glass, and at the same time, the next original is fed to and stopped at an image reading position to perform copying exposure. Such a procedure is repetitively performed. In this original conveying method, as the size of an original becomes smaller, an interval between two adjacent originals is increased, thus wasting conveyance time. This results in a decrease in copying speed.
If conveyance speed is increased more than a required level in order to solve the above problem, noise, wear of a conveyor belt, or the like becomes noticeable, and a damage to an original when a convey error occurs is also increased, resulting in a serious problem.
As inventions which can solve the above-mentioned drawback to some extent, original feeding methods of copying machines disclosed in, e.g., Japanese Patent Laid-Open (Kokai) Nos. 60-140364 and 61-32836 are known.
The original feeding method described in Japanese Patent Laid-Open (Kokai) No. 60-140364 is as follows. More specifically, when originals having a smaller size than a copying size are continuously copied, a first original placed on an original tray arranged at a side opposite to a platen glass (upstream side in an original conveying direction) is conveyed to a copying position (image reading position) set at a downstream position on the platen glass surface of a copying machine, and is stopped at that position while abutting against a stopper. Subsequently, a second original is conveyed to a standby position set at an upstream position on the platen glass surface adjacent to the copying position, and is stopped at that position while abutting against a stopper. The first original subjected to exposure is discharged in a downstream direction of the platen glass surface. In synchronism with this operation, the second original at the standby position is conveyed to the copying position, and a third original placed on the original tray is conveyed to and stopped at the standby position. Thus, such a procedure is repeated.
However, in the conventional original feeding method, since an original is stopped at the standby position by a mechanical stopper, A4-size originals (half a maximum size A3) can be efficiently conveyed. However, originals having a small size such as a B5 size or post-card size can only be held at a predetermined position of the stopper. Therefore, an interval between a reading original and the next original is increased more than required, thus impairing copying efficiency. In addition, in the conventional original feeding method, since the copying position on the platen glass is located at a position opposite to the original tray, conveyance time to the copying position of the first original requires a maximum conveyance time for a maximum size A3 original even if A4-size originals half the maximum size A3 are to be fed, resulting in poor work efficiency.
In contrast to this, the original feeding method described in Japanese Patent Laid-Open (Kokai) No 61-32836 is as follows. A distance slightly larger than a length of each of originals to be sequentially conveyed in a conveying direction is detected, and a conveyance time period required for moving a conveyor belt by the detected distance is set. A first original placed on an original tray is conveyed to and stopped at a copying position (image reading position) preset at a downstream position in the original conveying direction on a platen glass by a sheet feed roller and the conveyor belt. Subsequently, a second original is conveyed to and stopped at a standby position at an upstream position on the platen glass adjacent to the copying position with an appropriate interval by the sheet feed roller and the conveyor belt. Then, the first original subjected to exposure is discharged in a downstream direction of the platen glass surface. In synchronism with this operation, the second original at the standby position is conveyed to the copying position, and a third original placed on the original tray is conveyed to and stopped at the standby position by moving the conveyor belt by the corresponding convey time period. Thus, such a procedure is repeated. In this prior art, a positioning means for stopping an original at respective positions is realized not by a mechanical stopper but by stop position control of the conveyor belt. Since an interval between the reading original and the next original can be made constant regardless of the original size, the problem of a decrease in copying efficiency caused by the original size can be eliminated.
However, in the latter conventional method, for the second and subsequent originals, a procedure of conveying an original by a predetermined conveyance time period and stopping it at the standby position must be performed at least once. For this reason, as the number of times of repetition of conveying and stopping is increased, even if stop position control of the conveyor belt can be smoothly performed, an offset caused by slipping between the belt and the original tends to occur. Finally, the original is offset from a predetermined copying position when it reaches this position. As a result, stop precision as an important function of this original conveying apparatus is impaired.
Furthermore, in the latter conventional method, the problem of a decrease in copying efficiency caused by an original size difference can be eliminated, but it is difficult to control an original interval. More specifically, when the first original is conveyed and its trailing edge leaves an original tray unit, the second original is fed from the original tray. If the rotational speed of the sheet feed roller for feeding an original from the original tray is too fast, a feeding error such as skewing of an original tends to occur. For this reason, it is difficult to match the rotational speed of the sheet feed roller with the speed of the conveyor belt, and the rotational speed of the roller must be set to be lower than the speed of the conveyor belt. Therefore, an original interval is increased more than required, and becomes uniform regardless of an original size. However, this results in a poor copying efficiency.
The conventional method has no switching means for switching a normal mode for feeding originals one by one and the above-mentioned multi-feed mode. Therefore, when two originals (e.g., two A4-size originals) are placed on the platen glass, if image reading is executed for a maximum size (e.g., A3 size), an image on an original other than one for which image reading and image formation are to be performed is read. When the image is copied, an unnecessary image is copied.
In the conventional method, original interval control for performing an exposed original discharging operation and a sheet feeding operation of an original at the standby position by a single drive operation must also be performed. This control is complex, and it is difficult to shorten an original feed interval, resulting in poor efficiency.
Since an original before exposure is located at the downstream position on the platen glass on which an original which is being exposed is also present, a distance between originals cannot be shortened after an exposure operation is started. Therefore, the distance between the originals must be adjusted before the original is conveyed to the exposure position, thus causing loss time and difficulty in control. In order to shorten the distance between originals, the arrangement of drive units becomes complicated, and an original convey path also becomes complicated. In a worst case, an original may be damaged.